ra 
o 
196 Mr Potts, The Swarming of Odontosyllis. ' 
increased to a maximum when scores might be seen at once. The 
display waned somewhat more suddenly than it waxed. 
“The males and females differ considerably in size, the females 
often being twice as long as the males....Both sexes are distinctly 
phosphorescent—the female with strong and more continuous | 
glow and the male with sharper intermittent flashes. 
“Tn mating the females, which are clearly swimming at the 
surface of the water before they begin to be phosphorescent, show 
first as a dim glow. Quite suddenly she becomes acutely phos- 
phorescent, particularly in the posterior three-fourths of the body, 
though all the segments seem to be lumimous in some degree. At 
this phase she swims rapidly through the water in small luminous _ 
circles two or more inches in diameter. Around this smaller vivid | 
circle is a halo of phosphorescence growing dimmer peripherally, 
This halo of phosphorescence is possibly caused by the escaping | 
egos together with whatever body fluids accompany them. At | 
any rate the phosphorescent effect closely accompanies ovulation 
and the eggs continue mildly phosphorescent for a while. | 
“Tf the male does not appear this illumination ceases after 
10 to 20 seconds. In the absence of the male the process may | 
be repeated as often as four or five times by one female at | 
intervals of 10—30 seconds. The later intervals are longer than | 
the earlier. Usually, however, the males are sufficiently abundant 
to make this repetition unnecessary; and the unmated females — 
are rare, if they are out in the open water. One can sometimes 
locate the drifting female between displays by the persistence of | 
the luminosity of the eggs; but the male is unable to find her in’ 
this way. : 
“The male first appears as a delicate glint of light possibly as | 
: 
much as 10 or 15 feet from the luminous female. They do not swim | 
at the surface as do the females, but come obliquely up from the | 
deeper water. They dart directly for the centre of the luminous circle, _ 
and they locate the female with remarkable precision when she is | 
in the active stage of phosphorescence. If, however, she ceases to | 
be actively phosphorescent before he covers the distance he is 
uncertain and apparently ceases swimming, as he certainly ceases 
being luminous, until she becomes phosphorescent again. When 
her position becomes defined he quickly approaches. her, and they 
rotate together in somewhat wider circles, scattering eggs and 
sperm in the water. . The period is somewhat longer on the 
average than when the female is rotating alone; but it, too, 1s 
of short duration. 
“So far as could be observed the phosphorescent display is not 
repeated by either individual after mating. Very shortly the worms 
cease to be luminous and are lost.” 
This is, I submit, a very remarkable account. In its general 
